Transformer



Feb. 10,1931. R, J, EISEMAN' 1,191,719

TRANSFORMER Filed July 28, 1927 Iva/021lov- Robert J EzLsen/m Patented Pa. 10, 1931 UNITED STATES PATENT OFFICE ROBERT J. EISEMAN, OI CLEVRAND, OHIO, ASSIGNOB TO THE K. W. IGNITION COR- PORATION, OF CLEVELAND, OHIO, A CORPORATION OF OHIO TRANSFORMER Application filed July 28,.

This invention relates to improvements in transformers and has particular reference to small transformers adapted to be connected pended claims.

tohousehold lighting circuits for various purposes, as for example, for the purpose of supplying high voltage current to igniters of oil burning apparatus. My improved transformer has been designed especially'for this purpose.

The principal object of the invention is to provide certain improvements which very materially reduce the size and cost of the transformers and which at the same time result in a transformer having high efficiency and one that is particularly effective when employed for the special purpose mentioned above, namely, when employed with .an i'gniter.

The above objects are attained very effectively by my invention which enables me to very decidedly reduce the number of both the primary and secondary turns without increased heating and with reduced copper losses and "without otherwise adversely affecting the efficiency of the transformer, especially when employed with or as a part of an igniter. ing in the transformer a magnetic choke for the primary by the provision of a closed magnetic shunt around the leg which receives the primary winding, this magnetic shunt being of less cross sectional area than the remainder of the core, as hereinafter explained, so that the heretofore mentioned advantages are obtained.

The invention my be further briefly summarized as consisting in certain novel details of construction and combinations and arrangements of parts which will be described in the specification and set forth in the ap- In the accompanying sheet of drawings, the single figure shows the shape of the-core as actually used by me and shows conventionally the primary and secondary windings.

Referring now to the drawings, the core 10 which is formed, as usual of laminae or stampings, has two parallel legs 11 and 12 which receive, respectively, the primary winding 13 and the secondary winding 14.

This is accomplished by provid- 1927. Serial No. 208,941.

The primary winding is adapted to be connected to a lighting circuit and the secondary to a sultable spark gap device when the transformer is used for the purpose for which itwas designed, namely, as a part of the lgnit on apparatus of oil burners. However, it is not necessarily confined to this particular use. Ordinarily, this type of mary flux. It is to be understood, of course,

that this leg is integral with the remainder of the core, each lamina or stamping having this extra leg 15 and being of the shape shown in the drawing.

It is quite important to the attainment of the advantages stated and of the highest degree of efficiency that this leg 15 be considerably smaller in cross section than the legs 11 and 12 receiving the windings, and I find that the best results are obtained when the leg 15 has approximately 31 percent of the cross sectional area of the main legs 11 and 12, although the results are not very materially changed if the size of the auxiliary or shunt leg 15 compared with the legs 11 and 12 is altered somewhat, either increased or decreased, from the value or size-stated.

r I find that by this improvement I am ,enable d without suffering any disadvantages to reduce both the primary and the secondaryturns by approximately one-third. Obviously this enables me to reduce the size and to effect a very great saving in the cost by the reduction in the number of turns.

Furthermore, when the transformer is used with an igniter, the spark efficiency is not decreased by my improved transformer, but in fact is materially increased. While I am not sure that the following theory is correct,

I believe it is due to the fact that the rate of change of the magnetic flux at the time the igniting spark is obtained is very much more rapid than would be the case if the magnetic curve corresponded in shape to the electrical sine curve. I believe this is due to the fact that as the. current following the sine curve builds up in the, primary, part of the primary flux passes'through the main portion of the core, i. e., through the second ary leg 12, and part passes through the shunt leg 15, so that the magnetic flux builds up initially relatively slowly, but before the current reaches the peak of the sine wave, the

leg 15 becomes saturated, after which the rate of change of the flux in the leg 12 is more rapid, with the result that the rate of change of the flux threading through the secondary at the most effective part of the current sine wave is very rapid, as is desired for the production of an efficient-igniting spark, giving a higher voltage per turn on the secondary than the ordinary transformer.

I am not certain that the above theory is correct, but, nevertheless, I olfer it as the v best explanation known to me for the action or e'flect of the leg 15, in permitting a decided reduction in the number of turns of the primary and secondary windings and,

therefore, a decided reduction in the size and cost of the transformer without reducing its efliciency.

1Having thus described my invention, I

aim:

l. A transformer comprising a core having primary and secondary windings upon separate portions thereof and having a closed magnetic shunt around the portion of the core receiving the primary winding, said shunt having a less cross-sectional area than the remainder of the core, and the number of turns in each of said windings being materially smaller than would be required for a given output were the magnetic shunt omitted.

2. A transformer comprising a core having two legs receiving primary and secondary'windings and haying a third leg forming a closed magnetic shunt and of less crosss'ectional area than the legs receiving the windings, andthenumber of turns in each of said windings being materially smaller than would be required for a given output were "the magnetic shunt omitted.

3. A transformer comprising a core having three parallel legs, primary and secondary windings on two of the legs, the third leg being unwound and being at the end of the core outside the primary winding and adjacent thereto and forming with the leg receiving the primary winding a completely closed magnetic path, and the number of turns in each of said windings being materially smaller than would be required for a given output were the unwound leg omitted;

4. A transformer comprising a core, a closed principal magnetic path having primary and secondary windings therefor, and a closed magnetic shunt around the portion of the core receiving the primary winding, said shunt having a cross sectional area approxi mately thirty percent of that of the remainder of the core.

5. A transformer comprising a magnetizable core having a plurality of legs connected to form a closed magnetic circuit, a primary winding on one of said legs, 'a secondary winding on another of said legs, and a magnetic shunt connected in closed circuit with said legs, the number of turns of said windings being materially smaller than would be required for a given output were the magnetic shunt omitted.

In testimony whereof, I hereunto afiix my 

